**Abstract**

Pesticide covers a wide range of compounds including insecticides, fungicides, herbicides, rodenticides, molluscicides, nematicides, plant growth regulators, and others. Among them, organochlorine insecticides, used successfully in controlling a number of diseases, such as malaria and typhus, were banned or restricted after the 1960s in most of the technologically advanced countries. The introduction of other synthetic insecticides—organophosphate insecticides in the 1960s, carbamates in the 1970s, and pyrethroids in the 1980s, and the introduction of herbicides and fungicides in the 1970s–1980s contributed greatly to pest control and agricultural output. Ideally, a pesticide must be lethal to the targeted pests, but not to nontarget species, including man. Unfortunately, this is not the case, so the controversy of the use and abuse of pesticides has surfaced. The rampant use of these chemicals, under the adage, "if little is good, a lot more will be better" has played with humans and other life forms. The known ecological impacts of insecticides on terrestrial and aquatic ecosystems are reviewed in this chapter. Awareness of the impacts that insecticides are having in our world may help to introduce the management practices that aim at reducing and mitigating those impacts.

**Keywords:** pest control, insecticides, organophosphate, organochlorine, environment, human health
